1. Field of the Invention
This invention relates to a drive shaft apparatus for transverse engine vehicles, more particularly to a drive shaft apparatus for a front engine and front wheel drive vehicle in which a differential unit is offset from the center of the vehicle to one side of a left or right wheel (in the transverse direction of the vehicle).
2. Description of the Prior Art
In general, in a front engine and front drive vehicle having a transverse engine, a differential unit is often disposed in a position shifted from the center of the longitudinal axis of the vehicle toward a left or right wheel, because a trans-axle which is integrally composed of a clutch, a transmission and the differential unit is ordinarily placed at one end of the engine block. If, in this arrangement, left and right wheels are directly connected by drive shafts to the differential unit, these left and right drive shafts differ from each other in length and in cathedral angles (joint angles). When a drive shaft having a cathedral angle rotates a moment which acts to pivotally and inwardly move the wheel about a king pin, namely, a force which acts to inwardly steer the wheel is caused by the driving torque in accordance with the degree of the cathedral angle when the vehicle abruptly starts, accelerates or climbs. For this reason, if left and right cathedral angles are not equal, moments which act on the left and right wheels such as described above differ from each other so that the vehicle tends to be steered toward the wheel on the side of the longer drive shaft. The drive performance to linearly moving the vehicle is thereby reduced.
In consideration of this problem, a type of drive shaft apparatus for transverse engine vehicles has been proposed (such as that disclosed in Japanese Utility Model Laid-Open No. 107626/1982) which employs an intermediate shaft to equalize the length of the left and right drive shafts, thereby preventing the effect of torque steer such as described above.
More particularly in detail, as shown in FIG. 6, in a vehicle having a transverse engine 10 in which the center line X of the crank shaft extends in the transverse direction of the vehicle, the driving power is transmitted from a differential unit (not shown in the drawing) accommodated in a trans-axle case 18 mounted at one end of an engine block 16 to left and right wheels 12 and 14 through left and right drive shafts 22 and 24. Since this differential unit is mounted in a position largely shifted from the center axis of the vehicle in the transverse direction thereof, the drive shaft 22 which is disposed on the side where the distance between the wheel and the differential unit is smaller (on left hand side as viewed in FIG. 6) is directly connected to the differential unit in a conventional manner while the drive shaft 24 on the side where the distance between the wheel and the differential unit is larger (on the left hand side in FIG. 6) is connected through an intermediate shaft 26, thereby equalizing the length of the drive shafts 22 and 24. Incidentally, in FIG. 6, reference numerals 28 and 30 denote velocity joints disposed on the side of the differential unit, and reference numerals 32 and 34 denote velocity joints disposed on the sides of the wheels.
In the drive shaft apparatus thus arranged, the cathedral angles of the left and right drive shafts 22 and 24 are equalized so that equal moments act on left and right wheels 12 and 14, thereby eliminating the tendency to steer the vehicle.
In the arrangement of this type of apparatus, the intermediate shaft 26 is supported at its end portion, at which it is connected to the drive shaft 24, by a bearing 40 which is secured to a bracket 50 on an engine block 16, as shown in FIGS. 7 and 8. The intermediate shaft 26 is thus supported at its both ends thereof by the differential unit and the bearing 40, thereby increasing the apparatus stiffness (bearing stiffness):
The bearing 40 is previously forced along and set around the outer periphery of the intermediate shaft 26 and a snap ring 36 is applied thereto to prevent the bearing 40 from slipping off. A drive shaft assembly which is composed of the intermediate shaft 26, the velocity joint 30 disposed on the side of the differential unit, the drive shaft 24, and the velocity joint 34 disposed on the side of the wheel is mounted such that the top end of the intermediate shaft 26 is fitted into a side gear (not shown) of the differential unit while the bearing 40 is fitted into a through hole 52 of the bracket 50 which is secured to the engine block 16 by means of two bolts 54, a snap ring 38 being set in the bracket 50 to prevent the bearing 40 from being slipping off form the bracket.
However, in the drive shaft apparatus for transverse engine vehicles thus arranged, the bearing 40 and the through hole 52 are designed to be assembled in a loose-fit manner and a clearance 2S is provided between the bearing and the through hole for the purpose of facilitating the work of mounting the drive shaft assembly. That is, the size and weight of the drive shaft assembly which has the intermediate shaft 26, the velocity joint 30 disposed on the side of the differential unit, the drive shaft 24, and the velocity joint disposed on the side of the wheel is so large that the drive shaft assembly cannot easily be mounted while inserting the bearing 40 which is attached to the outer periphery of the intermediate shaft 26 into the through hole 52 of the bracket secured to the engine block 16 if the clearance 2S is not sufficient. It is thus necessary to set the clearance 2S more than a certain extent with a view to facilitating the assembling work and reducing the labor. The clearance 2S is exaggeratedly depicted in FIG. 8 so that it can be seen easily.
That is, there is a play between the inner surface of the through hole 52 of the bracket and the bearing 40 of the intermediate shaft. This play induces considerable rattling noise due to vibrations of the engine especially when the engine rotates in a medium speed range. Also there is a risk of creep wear or fretting wear of the bearing 40 caused by a whirling load or vibration of the intermediate shaft 26.
To prevent the problems due to the effect of the above-described fit clearance, the bearing may be forcibly inserted with a least clearance or, as disclosed in Japanese Utility Model Unexamined Laid-Open No. 107424/1985, a ring made of synthetic resin may be adapted. However, these methods inevitably result in the reduction of workability.